Simplify the following expression: $r = \dfrac{-7n}{8} - \dfrac{-9n}{8}$
Explanation: Since the expressions have the same denominator we simply combine the numerators: $r = \dfrac{-7n - (-9n)}{8}$ Combine like terms: $r = \dfrac{2n}{8}$ Simplify by dividing numerator and denominator by 2: $r = \dfrac{n}{4}$